The overall goal of this study is to combine in vivo and in vitro techniques to examine the role of neurotrophic factors on the survival, plasticity and regeneration of neurons. Regional neurotrophic activity in mature and aged rodent brain will be identified, quantified and purified. The initial focus will be on the survival-promoting activity found in the normal and in the damaged brain, which can be readily bioassayed using 8-day-old chick ciliary ganglon cells in culture. The basal levels of neurotrophic activity will be measured in various brain regions of the mature and aged rodent. The time course and extent of the injury induced increase in neurotrophic factor will be examined in normal and aged rat brain after surgical or kainic acid-induced lesions. The latter lesions will be used to mimic the type of damage found in certain types of human neural degenerative diseases. In addition, the chick ciliary ganglion assay will be used to measure neurotrophic and neurotoxic activities of extracts from the human brain or the CSF of normal and Alzheimer patients. While the chick ciliary bioassay will be the major assay employed, other assays are available and will be used as needed to examine neurotrophic and neurotoxic activities. For the in vivo studies, the ability of neurotrophic factors to enhance the survival of striatal transplants will be measured. Efforts to purify trophic factors will continue using a variety of biochemical procedures and the ciliary ganglion cells as a bioassay. The investigator will analyze 3H-glutamate binding cites in the aged brain using quantitative autoradiography on frozen sections of the rat and human brain. Digital subtraction quantitative autoradiography will be used to study the properties of glutamate receptors in slices from rat and human brain with special emphasis on the hippocampus. Specific binding of 3-H-glutamate defined with N-methyl-D-aspartate (NMDA) or 2-amino-4-phosphonobutyric acid (APB), 3H-kainic acid and 3H-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (3H-AMPA) will be used to identify four different subtypes of this receptor. The distribution and density of these sites will be compared in young and old Fischer 344 rats and in brains from normal persons and persons with Alzheimer disease.